One of their most valuable tools was a process called "geocoding," the conversion of street addresses into global positioning system (GPS) coordinates.

With streets flooded, street signs missing, and rescue crews unfamiliar with the Gulf Coast area, street addresses were not very useful.

"They would get phone calls, or the Coast Guard would come in with addresses in their hands and say, 'I need a latitude and longitude for this address.' So the GIS professionals would do a geocoding, give it to the Coast Guard who got on helicopters and saved lives," said Shoreh Elhami, director of GISCorps.

Elhami, co-founder of GISCorps, said that since 2004, the organization's volunteers have responded to disasters such as the Asian tsunami and Hurricane Katrina, as well as efforts to provide humanitarian relief, sustainable development, economic development, health, and education in all parts of the world.

The Corps had 20 volunteers on the ground in Mississippi less than 48 hours after Katrina's landfall.

GISCorps is part of URISA, the Urban and Regional Information Systems Association. Elhami said more than 900 qualified volunteers have GIS experience, and range from from city and state government officials to academics to people in private industry.

Volunteer Beth McMillan, a field geologist and professor at the University of Arkansas in Little Rock, worked in Pearl River County, Mississippi, a couple of weeks after the storm.

"A couple of days after the hurricane hit, I felt so down, and wondered what I could do. I could give a little bit of money, but that doesn't seem very satisfying. To be able to have a skill that can be used is much more empowering, it doesn't make you feel so helpless," said McMillan, back in Little Rock.

Although rescue efforts were over by the time she arrived, there were scores of other tasks she and her colleagues completed.

"We had laptops and map plotters, and a database that the group from the first week had put together. One map we produced showed cell phone towers in the county, and the estimated coverage of those towers. Everybody was communicating with cell phones and they needed to figure out where to go within the county to talk to one another," McMillan said.

McMillan described the volunteer efforts as a sort of "Maps to Go" for a wide range of people needing immediate information.

Their maps detailed road conditions, power outages, underground gas storage, and facilities with hazardous materials. Agencies from FEMA to the Red Cross to local utilities relied on the information that they constantly updated.

"This is how technology can make a difference," said David Shaw, director of the GeoResources Institute at Mississippi State University.

"It was a great team effort," said Shaw, for a crisis that he said had deteriorated into a Third World situation.

Shaw said he was amazed at the talent and the creativity of, basically, a roomful of strangers at these county Emergency Operations Centers. While eventually satellite links and Internet connections made the tasks easier, in some cases large amounts of data had to be driven several hours from one site to another.

Volunteers are never sure of the conditions they might face when deployed to disaster sites or developing countries. Assignments usually last between two weeks and two months. McMillan said her many experiences "roughing it" as a field geologist helped her deal with the living conditions in Mississippi.

"They said be prepared for really hot weather, and bring a sleeping bag," she said. "I slept in an empty U.S. Department of Agriculture building on a cot, with probably several hundred other people. But it did have power, bathrooms, and showers, so conditions were not as bad as they could have been," she said.

She and her colleagues ate MREs (military meals ready to eat) and worked 12-plus hour days every day.

"We did get a chance to tag along one afternoon with a couple of National Guardsmen from Mississippi on a trip to the coast. That was one of the most memorable experiences of my life. I've never seen such destruction, and the only way to really understand it is to see it in person," she said.